This disclosure relates to a fixer (fixing) ink containing water soluble or water dispersible amphoteric polymer for use with ink jet inks containing colorants. The disclosure also relates to a method of inkjet printing with this ink set.
Inkjet printing is a non-impact printing process in which droplets of ink are deposited on print media, such as paper, to form the desired image. The droplets are ejected from a printhead in response to electrical signals generated by a microprocessor.
Both dyes and pigments have been used as colorants for inkjet inks. While dyes are typically easier to formulate compared to pigments, they tend to fade quickly and are more prone to rub off. Inks comprising pigments dispersed in aqueous media are advantageously superior to inks using water-soluble dyes in water-fastness and light-fastness of printed images.
Pigments suitable for aqueous inkjet inks are in general well-known in the art. Traditionally, pigments were stabilized by dispersing agents, such as polymeric dispersants or surfactants, to produce a stable dispersion of the pigment in the vehicle. More recently though, so-called “self-dispersible” or “self-dispersing” pigments (hereafter “SDP”) have been developed. As the name would imply, SDPs are dispersible in water without dispersants.
One disadvantage of inkjet printers is the relatively slow speed compared to, for example, laser printers. The slow speeds are due in large part to the relatively slow dry time of inkjet inks as well as slow-down due to bleed control algorithms in the printer software.
Among the proposed solutions to increase print speeds is the formulation of inks for “fast drying” by inclusion of ingredients such as surfactants or other penetrants. These ingredients can indeed improve dry times by absorbing rapidly into the paper and in certain formulations reduce bleed, but usually cause edge acuity and optical density (OD) to decrease.
A fixer ink applied prior to the ink or right after the ink can be used to precipitate colorant and polymer contained in the ink, so that the precipitated colorants can stay or deposit on the paper surface, results in higher OD and better chroma.
A need still exists for an ink jettable fixer ink that is stable in a wide pH range and one that jets reliably allowing increased printing speeds while maintaining good print quality.